You can open Manage | External Datasources and edit the file references there to point to different files.
What you might experiment with is use this tool to list two sets of backend filenames in the relative path format:
What should happen is if you place this interface file in the same directory as DataFile1, it will connect to that file and if you place it in the same directory as Datafile2, it should connect to that one instead. The risk here is that nothing will automatically tell you which file is connected to your external data sources so it might be easy to get confused as to which data file is currently connected to your interface file.
Thanks for this advice. After experimenting with the external datasources menu, I think this will actually provide the functionality I need. I realized that the menu provides an abstraction since it allows me to name the external source independent from the file name. So, What I'll do is name the source "External Data" then point it to externaldata1.fp7. Then at another location I can just change the file to "externaldata2.fp7" since the data name stays the same nothing has to change in my design. It would be nice to be able to change datasources within a layout, but this should provide the functionality I need.